Open Source or Free wireframe tools

Question

Are there any open source or free wire framing tools available?

I tried Pencil, but are there any better ones?

mockingbird.com was awesome, but it's paid now from Aug 15th.

So, any other alternatives?

Thanks

Answer 1

I have used http://www.balsamiq.com/ with success. I do have Expression Studio from Microsoft, but there is currently no 'express' version (as far as I know).

UPDATE : I didn't realize that they are no longer free.

http://www.mashable.com has a list of a few, but I haven't tried them ... http://mashable.com/2010/07/15/wireframing-tools/